The semiconductor laser module is widely used as a light-source of an optical signal in an optical fiber transmission apparatus. In recent years, down-sizing of the optical transmission apparatus is progressing, and the highly integrated configuration of a circuit board is earnestly required. Accordingly, various circuit elements to be implemented on the circuit board have come to he miniaturized and the heights of them have become low. In view of the recent tendency in the circuit elements, the semiconductor laser module is required especially to be thinner. Although considerable efforts have been made on the aforementioned subject by engineers of optelectronics, further improvements are extremely desirable.